1. Field of the Invention
The present invention is related to a method of scanning backlight module driving lamps for an LCD, and more particularly, to a method of scanning backlight module driving lamps for an LCD by adjusting the frequency and duty cycle of the control signal.
2. Description of the Prior Art
Due to luminance of a conventional backlight module of an LCD being fixed and unvaried with time, the conventional backlight module of an LCD is prone to a “motion blur” phenomenon and the quality of the display image is thereby degraded. A scanning backlight module and related method are then derived to solve this problem. Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional scanning backlight module of a LCD. As shown in FIG. 1, an LCD panel 110 comprises three scanning sections 112, 114 and 116 and each scanning section corresponds to its own lamps 120 as the backlight source. The method for driving a conventional scanning backlight module of an LCD is described as below: in a first driving instance, the lamps 120a and 120b corresponding to the scanning section 112 are turned on, while the rest of the lamps are turned off; in the second driving instance, the lamps 120c and 120d corresponding to the scanning section 114 are turned on, while the rest of the lamps are turned off; in the third driving instance, the lamps 120e and 120f corresponding to the scanning section 116 are turned on, while the rest of the lamps are turned off; the above operation sequences are then repeated. For each scanning section, the display mechanism described above during a frame time is equivalent to inserting a blank frame and the motion blur issue can then be improved accordingly.
Please refer to FIG. 2. FIG. 2 is a diagram illustrating the signal waveforms of a conventional scanning backlight module of an LCD. As shown in FIG. 2, the signal S1 represents the control signal of the backlight module, the period D represents the duty cycle of the signal S1, the frequency F represents the frequency of the signal S1, the signal IL represents the operating current of the lamp, the signal LS represents the luminance of the lamp, the duration Tr represents the luminance raising time, and the duration Tf represents the luminance falling time. The on/off operation of the backlight module is controlled by the signal S1 and the ratio of the backlight module being turned on/off is determined by the duty cycle D. When the backlight module is turned on by the signal S1, the lamp requires the duration Tr to reach stable luminance, and when the backlight module is turned off by the signal S1, the lamp is darkened after the duration Tf. Due to the relatively long luminance raising/falling time required by the lamp, the effectiveness of using the black frame insertion method to improve the motion blur issue is limited.
As mentioned above, the driving method of the scanning backlight module of an LCD does not require all of the lamps 120 to be turned on simultaneously, therefore the overall luminance of the LCD is lower than that of the LCD with the conventional backlight module. For example, as shown in FIG. 1, the overall luminance and power consumption of the LCD with a scanning backlight module are approximately one third of the overall luminance and power consumption of the LCD with the conventional backlight module.
For improving the degraded overall luminance of the LCD with the scanning backlight module, a solution is to increase the luminance of the lamps 120. Increasing the luminance of the lamps 120, however, means the lamps 120 must be driven with a higher electric condition (a greater lamp current for example), and consequently decreasing the lifetime of the lamps.